SEOUL, South Korea (AP) — North Korea said Tuesday that leader Kim Jong Un has returned home from a trip to Russia where he deepened a “comradely fellowship and friendly ties” with President Vladimir Putin.

The official Korean Central News Agency didn’t give many specifics on the six-day trip that was Kim’s longest foreign travel since he took power in late 2011.

Kim visited several military sites in Russia and said in live comments last week that his country offered “full and unconditional support” to Putin. KCNA also said in an earlier report from his trip that Kim and Russian Defense Minister Sergei Shoigu discussed expanding “strategic and tactical coordination” between the countries’ armed forces.

His comments and itinerary raised concerns about possible arms deals, in which North Korea could supply ammunition to refill Russia’s drained inventory in the second year of the war in Ukraine in return for receiving Russian technologies to modernize his nuclear weapons arsenals. U.S. and South Korean officials have warned that Russia and North Korea would face consequences if they go ahead with such weapons transfers deals in violation of U.N. Security Council resolutions.

The new KCNA report said Kim’s train crossed a border river on Monday morning, but didn’t say whether he headed to the capital, Pyongyang, or elsewhere inside the country. Before traveling to Russia, Kim made several visits to his munitions factories, triggering speculation that he intended to check on productions of arms to be shipped to Russia.

While traveling through Russia’s far eastern region, Kim met Putin at Russia’s most important space launch center before visiting military sites to see some of Russia’s most advanced weapons systems such as nuclear-capable bombers, fighter jets and hypersonic missiles.

Many experts say Kim would seek to secure Russian help to acquire a sophisticated spy satellite, a nuclear-propelled submarine and powerful long-range missiles. But others say Kim would end up getting food and economic aid because Russia is reluctant to share its sensitive, high-tech weapons technologies with other countries.

Kim has been pushing hard to bolster his nuclear arsenal citing what he called intensifying U.S. military threats. Analysts say Kim would aim to use his enlarged arsenal to win greater concessions from the U.S. while boosting his military credentials at home in the face of economic hardships deepened over the COVID-19 pandemic.